QUESTION $5$

The Figure below shows a start$-$up heater used in ammonia unit to start$-$up the process.

For this system, the following statements are true $($select as many as appropriate$).$

a$.$ All the pneumatic control valves have a failure mode close.

b$.$ All the control valves have a failure mode open.

c$.$ There is a burner switch in place linked to a hand switch and a solenoid valve.

d$.$ The temperature of the hot gas is measured, whilst the fuel gas flowrate is manipulated.

e$.$ There is a pressure control loop in place.